Combined audio program and alarm signaling system with line supervision



Sept. l0, 1968 R. M. HEALD COMBINED AUDIO PROGRAM AND ALARM SIGNALINGSYST WITH LINE SUPERVISION Filed April 16, 1965 9 Sheets-Sheet l R M mn, m Y m TTPA/EVJT II I I I I I I I I I I I I I I I IIIrIIIIII Sept. 10,1968 R M. HEALD 3,401,234

COMBINED AUDIO PROGAM AND ALARM SIGNALING SYSTEM WITH LINE SUPERVISIONFiled April 16, 1965 9 Sheets-Shee'tI 2 x 3 B2?, M Q4/M,

Sept. 10, w68 R. M. HEALD 3,493,234

COMBINED AUDIO PROGRAM AND ALARM SIGNALING SYSTEM WITH LINE SUPERVISION@9J @ffy sept. 10, 968 R, Ml HEALD 3,401,234

COMBINED AUDIO PROGRAM AND ALARM SIGNALING SYSTEM WITH LINE SUPERVISION9 Sheets-Sheet 4 Filed Apr-i1 le, 1965 TTOPAEYS Sept. 10, 1968 COMBNEDAUDIO PRO R. M. HEALD WITH LINE SUPERVISION Filed April 16, 1965 GRAMAND ALARM SIGNALING SYSTEM 9 Sheets-Sheet 5 PAPE/MAW V Aaa/84e 2305z/mmey V fume @Mesurer 4044 2.3 233e HQ e l E-/O #Z3/e INVENTOR.

Sept. 10, 1968 R. M. Hr-:ALD 3,4%,234

COMBINED AUDIO PROGRAM AND ALARM SIGNALING SYSTEM WITH LINE SUPERVISIONFiled April 16, 1965 9 Sheets-Sheet 6 ,4 7 faQ/VE Sept. 10, 1968 R. M.HEALD I WITH LINE SUPERVISION Filed April 16, 1965 COMBINED AUDIOPROGRAM AND ALARM SIGNALING SYSTEM 9 Sheets-Sheet 7 @055 M HEQ Sept. l0,1968 R. M. HEALD 3,401,234

COMBINED AUDIO PROGRAM AND ALARM SIGNALING SYSTEM WITH LINE SUPERVISIONFiled Apljil 16, 1965 9 Sheets-Sheet 8 /358 BELL 335 I V I -II I/ i,

Jyf. 1N VENTOR.

United States Patent O 3,401,234 COMBINED AUDIO PROGRAM AND ALARMSIGNALING SYSTEM WITH LINE SUPERVISION Ross M. Heald, Winnipeg,Manitoba, Canada,

assignor to Rimac, Ltd.

Continuation-impart of application Ser. No. 246,808,

Dec. 24, 1962. This application Apr. 16, 1965, Ser. No. 448,695

17 Claims. (Cl. 179-2) This application is a continuation-in-part of mycopending application, Ser. No. 246,808, filed Dec. 24, 1962, and nowabandoned.

This invention relates to a signaling system for signaling between acustomers premises and an alarm central station.

In its most complete embodiment the system of the present invention hasprovision for transmitting alarm signals over a private two-wiretelephone line from a customers premises to an alarm central station andsimultaneously transmitting audio program signals, such as music, newsor announcements, over the same telephone line from the alarm centralstation to t-he customers premises. However, for situations where thecustomer is not interested in receiving the audio program signals forbroadcast at his premises but is interested in the alarm protectionservice, the present invention may be embodied in a less complete systemin which only the alarm signals are transmitted. Also, in such case thealarm signals may be sent by radio or microwave transmission, ifdesired. The alarm signals may be for tire, burglary and plant equipmentalarms, or any one or more of them.

Considered rst in its most complete system aspect, the present inventionis particularly advantageous in that it enables only a single two-wiretelephone line to transmit both alarm signals and audio program signalssimultaneously between the two stations. At each end of the line thealarm signals and the audio program signals are offectively separatedfrom each other, so that at the customers premises the audio programsignals may be broadcast over one or more loud speakers withoutinterference from the alarm signals, while at the alarm central stationthe incoming alarm signals may be received by alarm detection andrecording equipment there without interference from the audio programsignals originating there.

Whether by wire or by radio or microwave transmission, the alarm signalspreferably are transmitted continuously from the customers premises tothe alarm central station as long as there is no corresponding alarmcondition at the customers premises. A particular alarm signal stopswhen the corresponding alarm condition occurs. The use of such normallycontinuous alarm signals is advantageous in that it provides a fail-safesystem in which an equipment failure can be detected immediarab/ la herethe signal tr.1nsmission is over a telephone line, each type of alarm.signal (e.g., tire, burglary, and plant equipment) has a distinctivefixed frequency in the low audio range below 2000 cycles per second,preferably between 60 and 240 cycles per second, and ideally between 120and 180 cycles per second. Because the alarm signals are all within alow audio frequency range, the capacitive losses on the line (whichincrease directly with the frequency) are sutiiciently low as not toconstitute a practical limitation on the length of the telephone line,and thus the permissible distance between the alarm central station andthe customers premises, without requiring repeaters on the line. Also,interference or spurious alarm signals due to cross-fire or cross-talkon the telephone line are effectively eliminated by the use of ice lowaudio frequency alarm signals. Each alarm signal has a frequencysubstantially separated from 60 cycles per second and harmonics thereof,so that signals on nearby power lines cannot produce spurious alarmsignals on the telephone line.

At the alarm central station there is an alarm signal .-receiver foreach customers premises, and each such receiver has a separate alarmsignal detector for each type -of alarm service for that customer.

In accordance wit-h one aspect of the present invention, a novel visualdisplay arrangement is associated with each alarm signal detector forvisually indicating either a no-alarm or an alarm condition at thecorresponding customers premises and also having provision to be set bythe alarm central station operator to a standby con-dition after analarm condition at the customers premises has been signaled. Thisstandby condition prevails until the alarm has been answered and the11o-alarm signal tone restored. i

In accordance with another aspect of the present invention, the alarmsignal receiver has an amplifier with a reserve gain greater than themaximum attenuation of the alarm signals which may be caused by a singleline fault (i.e., either a ground or an open-circuit condition on eitherwire of the telephone line). Consequently, the alarm signaling systemcontinues to operate normally in the face of such a line fault.

In accordance with the preferred embodiment of the present invention theprovision of several different alarm tone signals over the line from aparticular customers premises to the alarm central station preventsspurious responses by the receiver there. Except in very unlikelycircumstances, there will 4always be at least one alarm signal on theline and this will prevent the amplifier in the receiver from going wideopen to its maximum possible amplification fact-or, whereby it mightamplify weak spurious signals on the line to a level where they mightproduce a spurious operation of one of the alarm signal detectors.

Another important aspect of the present invention is directed to a novelline supervision arrangement capable of detecting and indicating to thealarm central station operator a fault on either wire of the telephoneline. This line supervision arrangement is able to discriminate betweena line fault and any other type of equipment failure in the system.

A principal object of this invention is to provide a novel and improvedsignaling system for signaling between two stations.

Another object of this invention is to provide such a system in whichalarm signaling is performed in a failsafe fashion.

Another object of this invention is to provide such a system havingnovel provision for distinguishing a true alarm from an apparent alarmcaused solely by an equipment failure.

Another object of this invention is to provide such a system having anovel and advantageous alarm-indicating display arrangement at the alarmcentral station which may be set to a standby condition by the operatorthere, after an alarm Ihas been received, and which stays in thisstandby condition until the alarm condition at the customers premises(the remote station) has been corrected.

Another object of this invention is to provide a novel and advantageouspower supply arrangement for the alarm signal transmitter at thecustomers premises in such a system which insures that faulty operationof, or tampering with, this power supply will produce an equipmentfailure alarm and/ or burglar indication at the alarm central station.

Another object of this invention is to provide such a 3 system in whicha single two-wire telephone line transmits alarm signals from a remotestation to a central station while simultaneously audio program signalsmay be transmitted in the opposite direction over the line from thecentral station to the remote station for broadcast there.

Another object of this invention is to provide such a system havingnovel provision for detecting and' indicating a fault on the telephoneline.

Another object of this invention is to provide such a system which isadapted to maintain operation in the face of a single fault on thetelephone line.

Another object of this invention is to provide such a system which hasgreater freedom from interference by spurious signals, such as powerline signals, cross-talk" and cross-fire.

Another object of this invention is to provide such a system whichenables the use of longer telephone lines between stations without thenecessity of providing repeaters on the line.

Another object of this invention is to provide such a system having anovel fixed impedance matching unit at each end of the line to match theparticular line to the alarm signal transmitter at the customerspremises and to the alarm signal receiver at the alarm central station.

Another object of this invention is to provide such a system havingnovel provision for indicating an attack on the line by a would-beburglar or arsonist.

Further objects and advantages of this invention will be apparent fromthe following detailed description of two presently-preferredembodiments thereof, which are illustrated schematically in theaccompanying drawings.

In the drawings:

FIGURE 1 is a schematic block diagram of a preferred first embodiment ofthe present invention;

FIGURE 2 is a schematic circuit diagram of the power supply for thealarm signal transmitter at the customers premises in the FIG. 1 system;

FIGURE 3 is a schematic circuit diagram of the alarm signal oscillatorsand associated relay circuitry in the transmitter at the Customerspremises in the FIG. 1 system;

FIGURE 4 is a schematic circuit diagram of the alarm signal amplifierand filters in the transmitter at the customers premises in the FIG. lsystem',

FIGURE 5 is a schematic circuit diagram of the hybrid and the audioprogram receiver at the customers premises in the FIG, 1 system.

FIGURE 6 is a schematic circuit diagram of the hybrid and the line faultdetection circuitry at the alarm central Y station in the FIG. l system;

FIGURE 7 is a schematic circuit diagram of the filter and the amplifierin the alarm signal receiver 'at the alarm central station in the FIG. 1system;

FIGURE 8 is a schematic circuit diagram of the alarm signal detectorsand associated signaling circuitry in the receiver at the alarm centralstation in the FIG. 1 system;

FIGURE 9 is a schematic block diagram of the audio program transmitterand the alarm signal receiver equipment at the alarm central station ina second embodiment of the present system;

FIGURE 10 is a schematic circuit diagram of one of the alarm signaloscillators at the customers premises in this second system;

FIGURE 1l is a schematic circuit diagram of one of the alarm signaldetectors at the alarm central station in this second system;

FIGURE l2 is a schematic circuit diagram of a voice signaling circuit inthis second system for interrupting the normal audio program forannouncements or the like; and

FIGURE 13 is a schematic block diagram of the alarm signaling circuitryand the audio program receiver at the customers premises in this secondsystem.

d SYSTEM OF FrGUREs 1 8 Referring first to FIG. l, the preferred form ofthe present invention shown therein comprises at the customers premises(within the dashed-line enclosure 20) an alarm tone transmitterincluding a plurality of alarm signal generators, each having adistinctive, fixed, low laudio frequency output tone. In'the illustratedembodiment there are a fire alarm signal oscillator 21, a burglar alarmsignal oscillator 22, and al plant equipment alarm signal oscillator 23,although it is to be understood that there may be fewer or more of theseoscillators, depending upon the types of alarm service required by aparticular customer. Each of these oscillators is under the control ofvarious alarm sensing devices corresponding to that particular service.Each oscillator generates its distinctive output signal continuously aslong as the corresponding alarm condition has not occured. When thealarm condition occurs, operating the respective sensing device, thisturns off the corresponding alarm signal oscillator and the stopping ofthat alarm tone signals the occurence of that alarm condition.

Either the first alarm oscillator 21 or the burglar alarm oscillator 22,or both, may be interconnected with the plant equipment alarm oscillator23 so that if the former goes off because of a true alarm condition theplant equipment oscillator also will stop, whereas if the fire alarmoscillator or the burglar alarm oscillator stops because of an internalequipment failure, the plant equipment oscillator will not be turnedofi. This enables the operator Iat the alarm central station todistinguish between a true fire or burglar alarm and an apparent fire orburglar alarm due to an equipment failure, as described in detailhereinafter.

The three alarm tones are within the low audio frequency range below2000 cycles per second, preferably between 60 and 240 cycles per second,and ideally within the range from to 180 cycles per second andsubstanially separated from either of the latter. In one practicalembodiment the alarm tones have frequencies of 140, and 165 cycles persecond, respectively. Because the alarm tones are substantiallyseparated from 60 cycles per second and the latters second and thirdharmonics, this minimizes interference due to 60 cycles per second powersignals on power lines near the telephone line in the present system.Low audio frequency alarm tones are desirable because they enable theuse of longer telephone lines between the stations in the system withoutrequiring repeaters on the line to amplify the alarm tones. Also, theselow audio frequencies may be separated from the audio program signalscoming from the alarm central station without noticeable effect on thelistener at the customers premises.

The three -distinct alarm tones from the oscillators 21, 22 and 23 passthrough a common amplifier 24 at the customers premises and then throughan attenuating impedance arrangement 25 and an output filter 26 to ahybrid 27 connected to this end of the two-Wire telephone line. Asdescribed in detail hereinafter, the attenuating impedance arrangement25 is adjusted to match this telephone line to the alarm toneoscillators.

From the hybrid 27 at the customers premises the alarm signal tones passalong the two wires 131 and 133 of the telephone line to -a receiver atthe ialarm central station 28. These alarm tone signals are transversecurrents on the telephone line passing yfrom the hybrid 27 over one wireof the line to the alarm central station and returning over the otherwire of the telephone line, and not relying upon lground for a returnpath.

At the alarm central station 28 the alarm signal tones pass through asimilar hybrid 29, an attenuating impedance 30 (preferably with fixedcomponents), a filter 31 and a common amplifier 32 to three tonedetectors. These tone detectors preferably have respective reed relaysF-4, B-4 and E-4, respectively, which are tuned precisely to thedistinct frequencies of the alarm signal tones, so that each respondsonly to the corresponding alarm signal tone. These reed relays operaterespective alarm and reset relay circuits 33, 34 and 35, which operatealarm signaling arrangements, as described in detail hereinafter.

Each signaling arrangement includes a green lamp 216, 216b or 216e,which is on as long as the corresponding alarm tone is being received`(i.e., as long as the corresponding alarm condition has not occurred atthe customers premises). Each alarm signaling arrangement at the alarmcentral station also includes a red lamp 225, 225b or 225e, which is offas long as the corresponding alarm tone is being received and whichcomes on when the alarm tone stops.

The alarm signaling arrangement at the alarm central station alsoincludes a bell or other common audible alarm device which operates inresponse to the stopping of any one of the alarm tones.

Preferably, also, the alarm signaling arrangement at the alarm centralstation includes a reset arrangement by which the operator there, afteran alarm condition has been detected, may turn on the respective greenlamp (while the red lamp stays on) to indicate a standby condition,which prevails until the alarm condition at the customers premises hasbeen corrected. Simultaneously the common audible alarm device issilenced in preparation for receiving the next alarm.

Also, the alarm central station includes recording equipment whichautomatically records each alarm condition detected there.

In practice, of course, there will be a similar receiver at the alarmcentral station *for each of the other customers serviced by thisparticular alarm central station. The recording equipment will beconnected to rall of these receivers, so that one record sheet willcontain all of the alarms recorded in a given time period. Also,preferably, a bell or other sounding device will be connected to all ofthe receivers so as to audibly signal the operator at the alarm centralstation each time there is any type of alarm condition at any customerspremises.

At the alarm central station 28 there is also an audio program sou-rcewhich usually will -be a music program recorded on magnetic tape, withvoice announcements or news programs intersperse-d with the music. Thedetails of this audio program source may be varied for differentcustomer needs and interests, obviously.

This audio program is passed through the rejection filter 38 and thehybrid 29 at t-he alarm central station and is transmitted as transversecurrents over the twowire telephone line 131, 133 to the customerspremises 20. That is, the audio program signals pass from the alarmcentral station to the customers premises over one wire of the line,with the other wire providing the return, just as wit-h the alarm tonesignals coming from the customers premises. The audio program signalsand the alarm tone signals may be transmitted in this mannersimultaneously over the same telephone line.

At the alarm central station 28 the rejection filter 38 prevents theoutgoing audio program signals from passing through the hybrid 29 to thealarm tone receiver circuits.

At t-he customers premises 20 the incoming audio program signals passthrough the hybrid 27 and through a rejection filter 138 to a soundbroadcast system at the customers premises. The rejection filter 138prevents the alarm tone signals, which originate at the customerspremises, from passing through the hybrid 27 to the sound broadcastsystem there.

The customers premises also preferably is provided with a visual alarmsignaling system which signals any alarm conditions occurring there. Thealarm signaling system at the customers premises also preferablyincludes an audible alarm device or devices for fire and plant equipmentalarms.

The central station 28 also has a line supervisory or monitoringarrangement, described in detail hereinafter. This monitoring-arrangement includes means for applying a separate supervisory currentto each wire of the telephone line, as well as line alarm relays 37 anddistinctively colored indicator lamps 250 and 252 which tell whetherthere is a fault on either wire of the telephone line.

Keeping in mind the general operation of this system, the specificdetails of its different sections will now be considered.

Bower supply for alarmy tone transmitter at customers premises Referringto FIG. 2, the power supply for the alarm tone transmitter at thecustomers premises comprises a step-down transformer 40` having itsprimary winding con-v nected across a suitable 60 cycle per second,110-120 volt A.C. power supply. A center tap 41 on the secondary windingof this transformer is connected directly to ground. The opposite ends42 and 43 of this secondary windin-g are connected through therespective rectifier diodes `44 and `45 to the input terminal 46 of achoke input filter. The D.C. voltage from terminal 46 to ground is 21.5volts. The choke coil 47 and condenser 48 in the filter smooth therectified Voltage to substantially pure D.C.

Four transistors 49, 50, 51 and 52 and a rectifier diode 53 and a Zenerdiode 54 are interconnected to regulate the final D.C. output voltage,appearing across the output terminals 55 and 56 of the power Supply, at13.3 volts, regardless of variations in the A.C. line voltage applied tothe primary of transformer 40', or the temperature, or the load on thepower supply.

Two resistors 57 and 5-8 are series-connected between the input terminal46 of the choke filter and the base of transistor 49. A condenser 59 isconnected between ground and the juncture of resistors 57 and 58.Another condenser 60 is connected across the base and emitter oftransistor 49.

The emitter of transistor 49 is connected directly to the base oftransistor 50. A resistor 61 is connected between these electrodes andground.

The emitter of transistor 50 is connected directly to the basetransistor 51. A resistor 62 is connected between these electrodes andground.

The collector of each transistor 49, 50 and 51 is connected to thejuncture 63 of the choke coil 47 and condenser 48 in the choke inputfilter.

The emitter of transistor 51 is connected directly to the cathode ofrectier diode 53, The anode of this diode is connected directly to thenegative output terminal 55 of the power supply.

A resistor 64 and condenser 65 are connected in parallel with each otherbetween the anode of diode 53 and the base of transistor 52. A resistor66 and an adjustable resistor 67 are connected in parallel with eachother between the base of transistor 52 and the positive power supplyterminal 56. The collector of transistor 52 is connected directly to thebase of transistor 49.

A- resistor 68 and the Zener diode 54 are series-connected between thenegative and positive output terminals 55 ad 56 of the power supply. Theanode of Zener diode 54 is connected directly to the emitter oftransistor 52. The Zenerdiode 54 maintains a constant voltage dropacross itself, even in the event of variations in the current throughit. Therefore, it maintains the emitter of transistor 52 at apredetermined potential, regardless of any variations in the outputvoltage across 55 and 56.

If this negative output voltage were to attempt to increase in magnitudefor any reason (such as, in response to an increase in the A.C. powersupply voltage across the primary of transformer 4t), or a temperaturechange, or a change in the load across output terminals 55 and 56), thenthe voltage on the base of transistor 52 would increase, therebyincreasing the current through transistor 52. This assumed increasedcurrent would ow through resistors S7 and 58, decreasing the voltage onthe collector of transistor 52, as well as on the base of transistor 49.

Transistor 49 is connected as an emitter follower to transistor 50.Transistor 5t) is connected as an emitter follower to transistor 51.Transistor 51 is connected as an emitter follower to rectifier diode S3.Therefore, the assumed reduced voltage on the base of transistor 49would decrease the voltage on the emitter of transistor 49 and the baseof transistor 50, which would decrease the voltage on the emitter oftransistor t) and the base of transistor 5l, which would decrease thevoltage (negative) on terminal 5S, thereby cancelling out the attempt ofthis voltage to increase.

The reverse would hold true if the negative voltage at 55 were toattempt to decrease in magnitude.

Therefore, the output voltage across terminals 55 and 56 is preciselyregulated by this circuit. Preferably, resistor 67 is adjusted to setthis output voltage at 13.3 volts.

This power supply also includes a 13.3 volt standby battery 69 connectedacross output terminals 55 and 56. Normally, no current is drawn fromthis battery. Only in the event of a failure of the A.C. power supply totransformer 40 would current be drawn from this battery, in order tomaintain the alarm tone transmitter operating. Both sides of thisbattery are floating, i.e., neither is grounded. The positive batteryline is shown as a heavy line in FIG. 2.

The function of the rectifier diode 53 is to prevent the voltage ofbattery 69 from being applied to the emitter of transistor 51 if the AC. power supply fails. In that event, the voltage at this emitter willdrop to zero, thereby creating a plant equipment alarm.

Condenser 60 is adjusted to cause this regulator circuit to oscillate atabout 60 kilocycles per second if the standby battery 69 is removed fromthis circuit, either by tampering or by accident. In such event, 6() kc.signal of two volts peak-to-peak will appear across the power supplyoutput terminals 55 and 56 this creating a burglar alarm, as explainedhereinafter.

The emitter of transistor 51 is connected directly to an output line 70for a purpose explained later.

Alarm tone generators Referring to FIG. 3, the output terminals 55 and56 and the output line 70 of the just-described power supply are shownat the upper left corner of this figure. This figure also shows thethree oscillators or tone generators, one for the re alarm, the secondfor the burglary alarm, and the third for the plant equipment alarm.These oscillators generate respective tones of different low audiofrequencies, for example, 140, 150 and 165 cycles per second. Each ofthese oscillators is normally on-that is, it generates its distinctivefrequency tone in the absence of an alarm condition. When the alarmcondition occurs, then the respective oscillator stops, as explainedfurther hereinafter.

The fire alarm oscillator includes a frequency-sensitive vibratory reedF and two transistors F-l and F-Z. Reed F has a coil 71 whose impedanceis very high at the resonant frequencyof the reed.

A relay F-3 controls the operation of the tire alarm oscillator. RelayF-3 has a rst set of contacts consisting of a mobile contact 72 andspaced fixed contacts 73, 74. Normally (i.e., as long as the coil ofrelay F-3 is de-energized), contacts 72 and 73 are engaged. Mobilecontact 72 is connected to the negative power supply terminal 55. Fixedcontact '73 is connected through a green indicator lamp 75 to thepositive power supply terminal 56. Contact 73 also is connected directlyto a line '76 leading to the reed F and transistors F-l and F-Z.

VThe other, normally-open fixed contact 74 of this set is connectedthrough a red indicator lamp 77 to the positive power supply terminal56.

The lower end of the coil of relay F-3 is connected directly to terminal56. The upper end of this coil is connected through a plurality ofparallel-connected, normally-open switches 78 to the negative powersupply terminal 55. Each of these switches is arranged to be operated bya fire detection device, such as a smoke detector ortemperature-responsive device. While three such switches are shown forpurposes of illustration, it is to be understood that there will be asmany of such switches and fire detection devices as are necessary toprotect the customers premises.

The relay has a second set of contacts including a mobile contact 79 andan upper fixed contact S0 which is normally engaged by the mobilecontact (i.e., when F-3 is de-energized).

Relay F-S and switches 7S together constitute a re alarm conditiondetection means which turns off the iire alarm tone oscillator inresponse to the occurrence of a fire alarm condition at the cnstomerspremises (which closes one of the switches 73).

With this arrangement, normally (i.e., in the absence of a lire) theswitches 78 will all be open, the coil of relay F-3 will bedie-energized, relay contacts '72, 73 will be closed, relay contacts 79,8i? will be closed, the green indicator lamp will be on, and the redindicator lamp 77 will be off. When a fire occurs, one or more of theswitches 78 will close, thereby completing an energization circuit forthe coil of relay F-3. Relay contacts 72, 73 open and the green lamp 75goes out, relay contacts 72, 74 close and the red lamp 77 goes on toindicate at the customers premises the re alarm condition, and relaycontacts 79, 86 open.

If desired, a suitable holding circuit (not shown) may be provided tomaintain relay F-3 energized independent of the alarm switches 78 afterit has been initially energized by the closing of one of these switches.

Transistor F-l in the re alarm oscillator has its base connected throughthe coil 71 of reed F and a resistor 81 to line 76, which extends fromrelay contact 73. Another resistor 82 is connected between ground andthe juncture of resistor 81 and coil 71 of reed F. The collector oftransistor F-1 is connected through a resistor 83 to line 76. Theemitter of transistor F-1 is connected through a resistor 84 to thepositive power supply terminal 56. The collector of transistor F-l isconnected through a condenser 8S to the base of transistor F-2. A pairof parallel connected resistors 86 and S7 are connected between line 7 6and the base of transistor F-Z. A rectifier diode 88 is connectedbetween the base of transistor F-2 and the positive power supplyterminal 56. A resistor 89 is connected in parallel with this diode, asis a condenser 90. The collector of transistor F-2 is connected througha resistor 91 to line 76. The emitter of transistor F-Z is connectedthrough a resistor 92 to terminal 56.

The collector of transistor F-2 is connected back to the base oftransistor F-l through a positive feedback network including a resistor93, a condenser 94 and a resistor 9S, connected in series between thecollector of transistor F-Z and the base of transistor F-l. A condenser96 is connected between the positive power supply terminal 516 and thejuncture between resistor 93 and condenser 94 in the feedback network.

When D.C. power is first supplied to this oscillator, a small randomsignal occurs at the base of transistor F-1. This random signal isamplified by transistors F-l and F-Z, and is fed back Via the feedbacknetwork 93, 94, 95, 96 to the base of transistor F-l.

Reed F presents its highest impedance at its own resonant frequency.Therefore, the signal at the base of transistor F-1 will be a maximum atthe resonant frequency of reed F. Since there are two stages ofamplification, the signal is inverted twice and is fed back in phase tothe base of transistor F-l, so that the circuit oscillates. The feedbacknetwork 1:93-96 is so chosen as to insure that the reed F will vibrateat its main or fundamental frequency of resonance, and not at a higherharmonic. The oscillation is quite strong and causes transistor F-2 tobe overdriven, producing a square wave output signal 'at the fundamentalresonant frequency of reed F.

The function of diode 88 in the oscillator is to make transistor F-Zoverload uniformly on both the positive and negative half cycles of thesignal. This prevents the formation of second harmonic signals.

A pair of resistors 97 and 98, one fixed and one 'adjustable, areconnected in parallel with each other between the collector oftransistor F-2 and an output terminal T leading to a common amplier(FIG. 4). Another resistor 99 is connected between the collector oftransistor F-2 and terminal T.

In operation, as long as relay F-3 remains de-energized and the powersupply (FIG. 2) provides input power, the lire alarm oscillator willproduce square wave oscillations which are applied to terminal T in FIG.3. However, if one of the fire detecting switches 78 is closed, thenrelay F-3 will become energized and will disconnect the power supplyconnection (through its contacts 72, 73 and line 76) for the tire alarmoscillator.

The burglar alarm oscillator in FIG. 3 is basically the same as the firealarm oscillator and therefore will not be described in detail.Corresponding elements of the burglar alarm oscillator are given thesame reference numerals as those in the tire alarm oscillator, with a bsubscript added. In the burglar alarm oscillator the reed is given thereference character B, the transistors are B-1 and B-2, and the relay isB-3. In the burglar alarm oscillator there is no condenser correspondingto condenser 90 in the fire alarm oscillator. The burglar alarmoscillator has a condenser llb connected between line 76b and the baseof transistor B-l.

The relay circuit in the burglar alarm oscillator is different from thatin the tire lalarm oscillator in that burglar alarm relay B-3 isarranged to be energized normally (i.e., in the absence of an alamcondition) and to become de-energized in response to an alarm condition.The several burglar alarm switches 78b are normally closed and are allconnected in series with each other and in series with the coil of relayB-S across power supply terminals 55 and 56. With relay B-3 normallyenergized, its contacts 72b, 74h are closed, completing the energizationcircuit for the green lamp 75b and completing the circuit to line 76bleading to the burglar alarm oscillator.

Relay B-3 and switches 78b together constitute an alarm conditiondetection means which is operative to turn off the burglar alarmoscillator in response to the occurrence of a burglar alarm condition atthe customers premises (i.e., opening of a switch 78h).

If any one of the burglar alarm switches 78h is opened such as due tointrusion by a burglar, this de-energizes the coil of relay B-3. Relaycontacts 72b, 74h open, turning off the green lamp 75b and disconnectingthe power supply input to the burglar alarm oscillator, 'and relaycontacts 72b, 73b close to turn on the red lamp 77b.

If desired, a suitable holding circuit may be provided for maintainingB-S de-energized independent of the alarm switches 78b following itsinitial de-energization by the opening of one of these switches.

Except for the relay circuit, the burglar alarm oscillator operates inessentially the same manner as the lire alarm oscillator, generating asquare wave tone of slightly different frequency which appears at theterminal T except in the event of removal of the battery 69 in the powersupply (FIG. 2) or the opening of one or more of the burglar alarmswitches 78b.

The plant equipment alarm oscillator in FIG. 3 is basically similar tothe tire and police alarm oscillators, corresponding elements beinggiven the Same reference numerals with an e subscript added. In theplant equipment oscillator, there is no condenser corresponding tocondenser 90 in the tire alarm oscillator, and there is a condenser ltlecorresponding to condenser 100b in the burglar alarm oscillator.

The relay circuit for this oscillator is similar to that for the burglaralarm relay, except that the coil of relay E-3 is connected to beenergized from the output line 70 of the power supply (FIG. 2) through aseries of normallyclosed plant equipment alarm switches 78e back to thepositive power supply .terminal 56.

Relay E-3 and switches 78e together constitute a plant equipment alarmcondition detection means which Will turn off the plant equipment alarmoscillator in response to the occurrence of :a plant equipment alarmcondition at the customers premises (i.e., opening of a switch 78e).

The plant equipment alarm oscillator is interlocked with the tire alarmcondition detection means as follows:

The lower fixed contact 74e of relay E-3 is connected to mobile contact79` of relay F-S. Line 76e and the corresponding side of the greenindicator lamp 75e associated with relay E-3 are connected to fixedcontact 80 of relay F-3. As long as contacts 79, are closed (i.e., aslong as relay F-3 is energized, which is the n-on-alarm condition of thelire alarm oscillator), they complete an energization circuit for lamp75e and for line 76e of the plant equipment alarm oscillator.

Normally, therefore, in the plant equipment oscillator circuit relay E-Sis energized through the n-ormally-closed alarm switches 78e, and thegreen lamp 75e and line 76e are energized from line 70 through thenow-closed E-3 relay contacts 72e and 74e, and contacts 79 .and 80 ofrelay F-3. Consequently, the plant equipment oscillator is energized.Also, the red indicator lamp 77e is off because contacts 72e and 73e areopen. The distinctive frequency tones generated by the plant equipmentoscillator pass to the output terminal T which is common to all threeoscillators.

Opening of any one of the alarm switches 78e will deenergze the coil ofrelay E-3, de-energizing the plant equipment oscillator and also turningoff the green lamp 75e and turning on the red lamp 77e.

Also, if the voltage at the emitter of transistor 51 in the power supply(FIG. 2) drops to zero, as in the `case of a failure of the A.C. powerinput to transformer 40 or a failure of the power supply, relay E-3 willbecome deenergized, green lamp 75e will go out, and the power supply tothe plant equipment oscillator will be interrupted. Under theseconditions, the lire and burglar alarm oscillators will continue togenerate tones because battery 69 in the power supply will provide themwith input power. Therefore, such a power failure is sensed as a plan-tequipment failure or alarm condition.

If the battery 69 in the power supply (FIG. 2) is removed ordisconnected, the 60 kc. oscillations generated by the power supply, asalready described, will be applied by way of line 70` and condenser 100ein the plant equipment alarm oscillator to the base of transistor E-l inthe latter, causing the plant equipment oscillator to cease oscillatingand thereby producing a plant equipment alarm (no plant equipment alarmtone) condition at terminal T.

Also, these 60 kc. oscillations are applied by way of power supplyterminal 55 and condenser 10tlb in the burglar alarm oscillator to Ithebase of transistor B-l in the latter causing the burglar alarmoscillator to cease oscillating. Therefore, if an intruder were totamper with the battery connections in the oscillator power supply, theburglar alarm oscillator would stop, thereby indicating an alarmcondition.

In the fire alarm oscillator, condenser 90 prevents these 60 kc.oscillations in the power supply from turning off the re alarmoscillator. Therefore, the disconnection of battery 69 in the oscillatorpower supply, which would rarely, if ever, be due to a fire, does notturn off the ire alarm oscillator.

Due -to the described interlock between the fire alarm circuit and theplant equipment alarm circuit, an alarm condition in the fire alarmcircuit will also turn off the plant equipment oscillator, as well asthe green lamp 75e in the plant equipment alarm circuit as follows:

The fire alarm condition will energize the coil of relay 1:#3, asdescribed, causing its contacts 79t and 80 to open. This breaks theenergization circuit for line 76e leading to the plant equipmentoscillator and for green lamp 75e. Therefore, even though the plantequipment alarm switches 78e are closed and the coil of relay E-3 isenergized, the plant equipment oscillator and the green lamp 75e will gooff. (The red lamp 77e at the plant equipment oscillator will remainoff, also, as long as the coil of E-3 remains energized.)

The purpose of this interlock is to introduce deliberately 4a redundancyinto the system ot facilitate discrimination between a true fire alarmand an apparent fire alarm caused simply by an equipment failure. A truefire alarm condition will turn off both the fire alarm and plant equipPment yalarm oscillators, and this fact will be detected at the alarmcentral station. On the other hand, an equipment failure in the firealarm circuit which would turn off the fire alarm oscillator, but notthe plant equipment alarm oscillator, will be detected at the alarmcentral station as a fire alarm unaccompanied by a plant equipmentalarm, and this will be treated by the operator there as an equipmentalarm rather than a true fire larm.

A similar redundancy interlock Imay be provided between the burglaralarm circuit and the plant equipment alarm circuit to enable 4theoperator at the alarm central station to differentiate between a trueburglar .alarm and an equipment failure in the burglar alarm circuit.

Resistors 98, 98b and 98e in the outputs of the respective oscillatorsare adjusted to equalize the amplitudes of the fire, burglar and plantequipment alarm tones at terminal T.

Each of the relays F-3 and E-3 associated with the fire and plantequipment alarm oscillators, respectively, may operate audible .alarmdevices (not shown) at the customers premises, in addition to operatingthe red and green indicator lamps as described. In the case of theburglar alarm, however, normally it would not be desirable to providesuch `an audible alarm indication at :the customers premises becausethis would notify the burglar that his intrusion had been detected.

Common amplifier for alarmv ione generators Referring to FIG. 4, theamplifier shown therein arnplifies the distinctive frequency tonesgenerated respectively by the fire alarm oscillator, the burglar alarmoscillator and the plant equipment oscillator in FIG. 3.

This amplifier has a transistor 101 having its base connected directlyto the output terminal T which is common to all three oscillators, itscollector connected to the negative power supply terminal line 55, andits emitter connected through resistor 102 to the positive ypower supplyterminal 56. Transistor 101 operates as .an emitter follower. Acondenser 103, connected between terminal 56 and the base of transistor101, attenuates the harmonics of the square wave tones from theoscillators.

From transistor 101 the alarm tones pass through an input filter 104,which further attenuates the harmonics, and through a condenser 105 tothe base of a second transistor 106. An adjustable resistor 107 isconnected between terminal 55 and the base of this transistor, and aresistor 108 is connected between this base and terminal 56. A resistor109 is connected between the emitter of transistor 106 and terminal 56.

A driver transformer 110 has its primary winding 111 connected betweenterminal S5 and the collector of transistor 106. The secondary winding112 of this transformer has a center tap 113 connected to terminal 56. Apair of transistors 114 and 115 are connected in push-pull relationshipacross the transformer secondary 112, with the base of transistor 114connected to one end of the transformer secondary, the ybase oftransistor 115 connected to its opposite end, and the emitters of bothtransistors 114 and 115 connected to a center tap 113 on the transformersecondary, which is connected directly to the positive power supplyterminal 56. The respective collectors of transistors 114 and 115 areconnected to the opposite ends of the primary winding 116 of an outputtransformer 117. Input transformer 110 matches transistor 106 to thebases of the pushpull transistors 114 and 115. Transistors 114 and 115operate as class B power transistors, each conducting on only its halfcycle. The alarm tones are amplified by this push-pull stage and areapplied to the output transformer 117.

The secondary winding 118 of output transformer 117 has a center tap 119which is connected via an adjustable resistor 120 to the emitter oftransistor 106. This provides negative feedback to transistor 106, andresistor 120 is adjusted to provide the desired overall amplifier gain.

A condenser 121 is connected across the secondary winding 118 of theoutput transformer 117 to insure the stability of the amplifier.

The alarm tones then pass through a voltage divider 122, 123 to theinput terminal 124 of an output filter 125. This filter is a two-stagefilter having a pass band of 130 to 170 cycles per second. All harmonicsin the alarm tones are removed in this filter. The alarm tones comingout of filter 125 are applied across a winding 126 of a hybrid at thecustomers premises which couples the equipment there to the two-wiretelephone line extending between the customers premises and the alarmcentral station.

An adjustable condenser 127 is connected between the output terminal 128of the output filter and the positive power supply terminal 56. Thiscondenser is adjusted to present the correct impedance from thetelephone line to the output filter 125.

The voltage-dividing resistors 122, 123 constitute an attenuator andmatching circuit, which preferably is positioned in a matching plug atthe alarm tone transmitter. The values of these components are chosen soas to match the combined overall impedance and line characteristics ofthat plug and the particular two-wire telephone line (between thetransmitter and the alarm central station) to the transmitter, so as toprovide proper level in the transfer of the alarm tones from thetransmitter to that particular line, thus providing interchangeabilityof transmitters without line adjustments.

Hybrid and rejection lter al customers premises Referring to FIG. 5, thehybrid at the customers premises comprises a first pair of identical,series-connected windings 129e and 129b and a second pair of identical,series-connected windings 130e and 130b, all inductively coupled to theaforementioned winding 126. The lower end of winding 129b is connecteddirectly to one wire 131 of the two-wire telephone line which extendsbetween the customers premises and the alarm central station. The upperend of winding 130e is connected through a resistor 132 to the otherwire 133 of this two-wire telephone line.

A balancing network 134, preferably composed of resistors andcondensers, is connected between the upper end of winding 129a and thelower end of winding 130b. Network 134 presents an impedance which issubstantially matched to the impedance of the two-wire telephone line atthe frequency of each of the three alarm tones.

The hybrid also includes a pair of windings 135 and 136, bothinductively coupled to a winding 137. The latter is connected through arejection filter 138 and an amplifier 139 to one or more loud speakers140, which broadcast at the customers premises the musicor otherprograms coming over the two-wire telephone line 131, 133 from the alarmcentral station. The rejection filter 138 rejects all signals within thenarrow frequency band occupied by the alarm tones, so that any alarmtone signals which may happen to pass through the hybrid to winding 137are positively prevented from passing to the loudspeakers 140 at thecustomers premises. Except for this relatively narrow bandwidth, whichis chosen to be hardly noticeable by program listeners at the customerspremises, the program signals pass to the loudspeakers 140.

The hybrid also operates to separate the program signals from the alarmtone signals at the customers station, as explained hereinafter.

The upper end of winding 135 is connected directly to a center tap 141between windings 129a and 129b. The lower end of winding 135 isconnected to ground through parallel-connected resistors 142, 143 andcondensers 144, 145. Resistor 142 and condenser 145 are adjustable.Condensers 144 and 145 effectively short-circuit the lower end ofwinding 135 to ground for A.C. Resistors 142 and 143 complete a path toground for D C. supervisory current on wire 131 of the telephone line,as explained hereinafter.

Similarly, the lower end of winding 136 is connected directly to acenter tap 146 between windings 130a and 130b. The upper end of winding136 is connected to ground through parallel-connected resistors 147, 148and c0ndensers 149, 150. Resistor 147 and condenser 150 are adjustable.Condensers 149 and 151) effectively shortcircuit the upper end ofwinding 136 to ground for A.C. Resistors 147 and 148 complete a path toground for D C. supervisory current on wire 133 of the two-wiretelephone line, as explained hereinafter.

This hybrid is basically a bridge which separates the three alarm fromthe program coming in over the telephone line. The alarm tones aresubstantially completely suppressed in going from the input winding 126to the output winding 137 of the hybrid, but they are passed withoutexcessive attenuation to the two-wire telephone line 131, 133. Theprogram signals coming in over the telephone line pass without excessiveattenuation through the hybrid to the output winding 137 and thence tothe loud speakers 140.

Considering the alarm signals only, each alarm tone on winding 126induces first and second secondary currents in windings 129a and 129b,respectively, which are equal if network 134 properly matches thetelephone line impedance at this signal frequency. The first secondarycurrent (in winding 129g) iiows from mid-tap 141 through winding 129a,balancing network 134, Winding 13012, and from mid-tap 146 throughwindings 135 and 135 (which are effectively in series to A.C.) back tomid-tap 141. The second secondary current (in winding 129b) ows frommid-tap 141 through windings 135 and 136, winding 13a, through theimpedance of the telephone line 133, 131, and from there through winding129b back to mid-tap 141. These two secondary currents are equal andopposite through windings 135 and 136. Therefore, they produce no netvoltage across windings 135 and 136, and they induce no net voltageacross winding 137. Consequently, the alarm tone is not applied to theloudspeakers 140 at the customers premises. The second secondary current(in winding 1Z9b) goes to the telephone line, as described, to producethe alarm tones at the alarm central station (at the other end of theline).

In practice, the energy loss of the alarm tones in this hybrid inpassing from the alarm tone transmitter to the telephone line is onlyabout 3 decibels.

Considering the program signals only, these signals may be assumed tocome in over wire 131 of the telephone line to winding 129]; and toreturn to the other wire 133 of the telephone line from winding 130er.If the impedance across winding 126 looking to the left in FIG. 5 (i.e.,toward the alarm tone transmitter) substantially matches the impedanceof the telephone line for a given program signal frequency, then thisprogram signal will flow through winding 12%, mid-tap 141, windings and136 (which are effectively in series to A.C.), mid-tap 146 and winding130g back to wire 133 of the telephone line without being attenuatedsignificantly. For certain frequencies of the program signals, however,this substantial impedance match will not exist, and in that case theincoming program signal will divide at mid-tap 141, with part going towindings 135, 136 and the remainder going through network 134. However,in either case the incoming program signals produce a substantialcurrent through windings 135, 136, which induces a voltage acrosssecondary winding 137 so that the program signals are broadcast at theloud speakers 140 at the customers premises.

In practice, it has been found that the attenuation of the programsignals in the present system is substantially independent of theimpedance of the alarm tone transmitter connected across winding 126.

Hybrid at alarm central station Referring to FIG. 6, at the alarmcentral station the alarm tones coming from the customers premises overthe two wire telephone line are passed through a hybrid which isgenerally similar to the hybrid (FIG. 5) at the customers station. Thishybrid at the alarm central station passes the incoming alarm toneswithout excessive attenuation to an alarm signaling circuit there. Also,this hybrid passes the program originating at the alarm central stationto the two-wire telephone line without excessive attenuation. Rejectionlter 38 prevents the program from passing to the alarm signaling circuitat the alarm central station.

This hybrid comprises a winding 161 connected across the program source162, which broadcasts a program of music and/or voice messages, such asannouncements or news. A first pair of windings 16311, 16317 and asecond pair of windings 164a, 164-b are inductively coupled to winding161. The lower end of winding 163!) is connected directly to one wire133 of the two-wire telephone line. The upper end of winding 164e isconnected directly to the other wire 131 of the telephone line. Theupper end of winding 163a and the lower end of winding 164b areconnected to the opposite terminals of an impedance matching network165.

The hybrid also includes a pair of primary windings 168 and 169 and asecondary winding 170, which is inductively coupled to both primarywindings 168, 169 and is connected to an alarm signaling circuit, to bedescribed later. The upper end of winding 168 is connected directly to amid-tap 171 between windings 163g and 16315. The lower end of the otherprimary winding 169 is connected directly to a mid-tap 172 betweenwindings 16451 and 164b. The lower end of winding 168 is connectedthrough a pair of parallel-connected condensers 173, 174 to ground,condenser 174 being adjustable. The upper end of winding 169 isconnected through a pair of parallel-connected condensers 175, 176 toground, condenser 176 being adjustable. These condensers effectivelyshortcircuit the lower end of winding 168 and the upper end of winding169 to ground for A.C.

This hybrid also is basically a bridge which separates the threeincoming alarm tones from the outgoing program signals. The incomingalarm tones are Ipassed from the telephone line 131, 133 through thishybrid to the output winding 170 without excessive attenuation. At thesame time, the program signals from source 162 are passed to thetelephone line without excessive attenuation and are more or lesscompletely attenuated in attempting to pass through the hybrid to theoutput winding 170.

The terminating condensers 173-176 in the hybrid (FIG. 6) at the alarmcentral station and the terminating condensers 144, 145, 149, in thehybrid (FIG. 5) at the subscribers station terminate the respectivewires i of the telephone line to ground for A.C. They are so chosen thatsubstantially the same attenuation of the alarm signals will be producedby either an open-circuit or a ground fault on either wire of thetelephone line. This attenuation is more than offset by the reserve gainof the amplifier (FIG. 7) at the alarm central station so as not tointerfere with the continued detection of the alarm tones there in theevent of such a fault on the telephone line.

Amplifier and band pass filter at alarm central station From the outputterminals 177, 178 of winding 170 in FIG. 6, the incoming alarm tonespass to a voltage divider or attenuator composed of resistors 180, 181(FIG. 7). After being reduced in amplitude in this voltage divider, thealarm tones pass through the band pass filter 31 having a pass band offrom 135 to 170 c.p.s. From this filter the three alarm tones passthrough an amplifier (32 in FIG. l) including transistors 183, 184, 185,186 and 187 in FIG. 6.

Preferably', resistors 180, 181 are fixed resistors in a removable plugat the receiver. They are chosen to match the overall combined impedanceof the particular telephone line and this plug to the receiver formaximum transfer of the signal energy between the line and the receiver.

The band pass filter 31 passes the alarm signal tones withoutsubstantially attenuation. Thus, this band pass filter helps theseparation of the yprogram signals from the alarm tone signals at thealarm central station.

Preferably, as already mentioned, the alarm tone signals are within afrequency range between 120 and 180 cycles per second and substantiallyspaced from both of these frequencies. The pass band of the band passIfilter 31 is within this same frequency range, so that this filterprevents 60` cycle per second power line signals or harmonics thereoffrom passing to the alarm tone detection circuits.

One output terminal 188 of the band pass filter 31 is connected directlyto the base of the first transistor 183. This transistor has a highinput impedance due to a large resistor 189 connected between itsemitter and ground. The other output terminal 190 of lfilter 31 isconnected through a pair of parallel-connected, adjustable resistors 191and 192 to a line 196.

A rectifier diode 193e is connected between line 196 and the base oftransistor 183. Another rectifier diode 193b of the same polarity isconnected between the base of transistor 183 and ground. Normally,diodes 193a and 193b are non-conducting and have no effect on theamplifier. However, in the event of a high transient voltage on thetelephone line 131, 133, such as due to a power hit or lightning strike,they protect transistor 183 against damage.

A resistor 195 is connected between the output terminal 190 of filter 31and ground. An adjustable resistor 194 is connected between line 196 andthe collector of transistor 183.

i The collector of the first transistor 183 is connected directly to thebase of the second transistor 184 in this amplifier. The collector oftransistor 1814 is connected directly to line 196. A resistor 197 isconnected between the emitter of transistor 184 and ground. The emitterof the second transistor is coupled to the base of the third transistor185 through a condenser 198.

A pair of resistors 199 and 200 (199 being adjustable) are connectedbetween line 196 and the base of transistor 185. A resistor 201 isconnected between this base and ground. A resistor 202 is connectedbetween the emitter of transistor 185 and ground. A resistor 203 isconnected between the collector of transistor 185 and line 196. Thecollector of the third transistor 185 is coupled through aparallel-connected resistor 204 and condenser `205 to the base of thefourth transistor 186 in the amplifier.

The base of transistor 186 is connected through a resistor v206 toground. A resistor 207 is connected between line 196 and the collectorof transistor 186. A resistor 208 is connected between the emitter oftransistor 186 and ground. The emitter of the fourth transistor 186 inthis amplifier is connected directly to the base of the fifth transistor187.

The collector of transistor 187 is connected to line 196 through aresistor 209, and the emitter is connected through a resistor 210 toground.

The output signals from the amplifier appear across lines 211 and 212,which are connected respectively to the collector and emitter of thefifth transistor 187.

In the operation of this amplifier at the alarm central station, thethree incoming alarm tones, after passing through the hybrid of FIG. 6,are amplified by transistors 183-187. Transistors 185, 186 and 187, inaddition to amplifying, limit and square off the three tones. Theamplitude level of the output from transistor 187 remains substantiallyconstant over a 20 decibel range of the input signals to the amplifier.That is, the amplifier has a reserve gain of 20 db. Consequently, thealarm tone output signals from this amplifier have a substantiallyconstant level or amplitude even in the event of attenuation due to afault on the telephone line or some other reason.

The three different alarm tone frequencies are unequally spaced.Preferably, one is at 14() c.p.s., a second at 150 c.p.s., and the thirdat 165 c.p.s. The reason for this is that the receiver amplifier inlimiting or clipping these incoming alarm tones also produces sum anddifference frequency signals. Therefore if the signals were 140, 150 and160 c.p.s., for example, and if only the 150 and 160 c.p.s. alarm toneswere present on the telephone line, they could combine to produce aspurious 140 c.p.s. signal in the amplifier, so that the alarm centralstation would not detect the absence of the 140 c.p.s. tone on the line.This is positively avoided by providing unequal frequency spacingsbetween the lower, -middle and higher frequency alarm tones.

Line fault monitoring circuit Referring again to FIG. 6, the two-wiretelephone line 131, 133 is monitored for faults by a D.C. supervisorycircuit connected to the hybrid at the alarm central oftice. Thissupervisory circuit includes a pair of two-coil relays 240 and 241.

Relay 240 has a first coil 242 having its lower end connected to thevolt negative terminal of a battery 243 through a fuse 271. The upperend of this coil is connected through a pair of parallel-connectedresistors 244 and 245 to ground. The positive terminal of battery 243 isgrounded. The second coil 246 of relay 240 has its lower end connectedto the negative terminal of battery 243 through a fuse 270. The upperend of coil 246 is connected to a normally-closed fixed contact 247 ofthe other two-coil relay 241.

Relay 240 has a grounded mobile Contact 248, a normally-closed fixedContact 249 connected through a green indicator lamp 250 to theaforementioned line 196, and a normally-open fixed contact 251 connectedthrough an amber indicator lamp 252 to line 196. Line 196 is negativewith respect to ground. The two coils 242 and 246 of relay 240 arearranged to produce equal and opposite ampere turns of magnetic fluxwhen both are energized by normal current. Resistor 245 is adjustablefor this purpose. These coils jointly control the position of mobilecontact 249. When both coils 242 and 246 are energized normally, theirrespective fluxes cancel each other and the mobile contact 248 engagesfixed contact 249, as shown in FIG. 6. However, when coil 246 isenergized by an abnormally high or low current, as explainedhereinafter, the resulting flux unbalance in relay 240 will cause thelatter to move the mobile con- 17 tact 248 out of engagement with fixedcontact 249 and into engagement with fixed contact 251.

A diode 253 is connected between the normally-open fixed contact 251 ofrelay 240 and a line 254 leading to a line alarm indicator device.

The second relay 241 has a pair of coils 255 and 256. The lower end ofcoil 255 is connected through a fuse 272 to the +90 volt positiveterminal of a battery 257, whose negative terminal is grounded. Theupper end of coil 255 is connected through an adjustable resistor 258 tothe upper end of coil 169 in the hybrid at the alarm central ofce. Theother coil 256 of relay 241 has its lower end connected through a fuse273 to the positive terminal of battery 257 and its upper end connectedto ground through a pair of parallel-connected resistors 259 and 260,resistor 260 being adjustable.

Relay 241 has the already mentioned normally-closed fixed contact 247, amobile contact 261 connected 'through an adjustable resistor 262 to thelower end of coil 168 in the hybrid at the alarm central ofiice, and anopencircuited, normally-open fixed contact 263.

The two coils 255 and 256 of relay 241 are arranged to produced equaland opposite fluxes when both are energized by normal current. Resistor260 is adjusted to provide this equalization. These coils 255 and 256jointly control the position of the mobile contact 261. When both areenergized normally, mobile contact 261 engages fixed contact 247 asshown. When coil 255 is energized by abnormally high or low current, theresulting flux unbalance in relay 241 causes the latter to move mobilecontact 261 into engagement with the other fixed contact 263.

Normally (i.e., in the absence of a line fault), the negative polarityD.C. current from battery 243 iiows through coil 246 of relay 240 andthence through the normally-closed contacts 247, 261 of relay 241,resistor 262, and through the windings 168 and 163b in the hybrid at thealarm central station to wire 133 of the twowire telephone line. At thecustomers premises (at the other end of the telephone line) thisnegative D.C. current fiows through windings 130a and 136 in the hybridthere (FIG. and thence through resistors 147, 148 to ground.

The green indicator lamp 250 at the alarm central ofiice is energizedfrom line 196 through relay contacts 249, 248 to ground at this time.The amber indicator lamp 252 is off. v

Normally, also, the positive polarity D.C. current fiows from battery257 (FIG. 6) at the alarm central office through coil 255 of relay 241,resistor 258, and through winding 169 and winding 164a in the hybrid atthe alarm central office to wire 131 of the two-wire telephone line. Atthe other end of the line (FIG. 5), this positive D.C. current flowsfrom wire 131 through winding 129b in the hybrid to mid-tap 141 andthence through winding 135 there and thence through parallel-connectedresistors 142, 143 to ground.

Under these normal (i.e., no line fault) conditions, the net flux ofrelay 240 is substantially zero so that its contacts 248, 249 areengaged, and the net flux of relay 241 is substantially zero so that itscontacts 261, 247 are engaged.

In the event that the telephone line wire 133 becomes fully or partiallyopen-circuited, the current through coil 246 will decrease and relay 240will operate due to the fiux unbalance at its coils 242 and 246. Relay240 moves its mobile contact 248 out of engagement with contact 249 andinto engagement with contact 251. The opening of contacts 248, 249causes the green lamp 250 to go off. The closing of contacts 248, 251causes the amber lamp 252 to go on, this lamp now being energized fromline 196 through contacts 251, 248 to ground. The closing of contacts248, 251 also connects diode 253 to ground and causes the alarm deviceon line 254 to be operated.

In the event that the telephone line wire 133 becomes fully or partiallygrounded, the current through coil 246 18 will increase to an abnormalvalue and relay 240 will Operate due to the flux unbalance between itscoils 242 and 246, turning off the green lamp 250, turning on the amberlamp 252 and operating the audible alarm device on line 254 by groundingdiode 253.

If either an open-circuit or grounded condition, cornplete or partial,occurs on the other telephone line wire 131, there will be either acurrent decrease or increase in coil 255 of relay 241, unbalancing thefluxes in this relay and causing it to open its contacts 261, 247. Theopening of these contacts breaks the energization circuit for the coil246 of relay 240. Consequently, relay 240 operates, turning off thegreen lamp 250, turning on the amber lamp 252, and operating the audiblealarm device on line 254.

When the line fault is corrected, the respective relay 240 or 241associated with that particular wire of the telephone line automaticallyis restored to the normal (no line fault) condition by virtue of thefact that the opposing fiuxes in its two coils will be equalized.

At the subscribers station, FIG. 5, the terminating resistors 142, 143and 147, 148 maintain the respective wires 131 and 133 of the telephoneline at D.C. potentials substantially different from ground, so that theexistence of leakage or a short circuit to ground of either wire at ornear the subscribers station will be detected by the line faultmonitoring circuit of FIG. 6. Because of the terminating condensers 144,145 and 149, 150, these resistors are not a significant factor in theA.C. circuitry.

Separate fuses 270, 271, 272 and 273 are connected in the respectivelines from batteries 243 and 257 to relay windings 246, 242, 256 and255. Therefore, the line fault alarm will operate in the event of afault in any of these lines from the respective battery to a relaywinding. This insures that the line alarm will be in working order, orelse the alarm will operate the same as if a fault had actually occurredin the telephone line.

Since both a positive battery 257 and a negative battery 243 are used toapply separate individual D.C. supervisory currents to the telephoneline wires 231 and 233, respectively, the ground is not used and thus noground currents exist to cause erosion effects.

If both wires of the telephone line are cut or are shorted to eachother, this will be detected by the D.C. supervisory circuit justdescribed and also it will stop all of the alarm signal tones on thisline, causing all of the red alarm lamps for that customer to light upat the alarm central station where it will be treated as a burglaralarm. Therefore, a deliverate attack on the line by a would-be burglaror arsonist will be detected in a distinctive and unique manner at thealarm central station in that the liue supervisory alarm and theburglar, fire and plant equipment alarm lights will all be operated.

Alarm tone detectors at alarm central station' Referring to FIG. 8, theoutput signals from the amplifier of FIG. 7 are applied via terminals211 and 212 to three reed relays F-4, B-4 and E-4, respectively. Reedrelay F-4 is tuned precisely to the frequency of the fire alarmoscillator tones, and B-4 and E-4 are similarly tuned respectively tothe burglary and plant equipment alarm tone signal frequencies.Therefore, these reed relays effectively detect and separate from oneanother the three different incoming alarm tones.

The lower end of the coil of reed relay F-4 is connected directly toline 211 from the collector of the final transistor 187 in the FIG. 7amplifier. The upper end of this relay coil is connected through abiasing resistor 213 to the other output line 212 from the amplifier.Also, the upper end of this relay coil is connected through a resistor196f to the aforementioned line 196.

The respective coils of reed relays B-4 and E-4 have similar connectionsto the amplifier output, so that the 19 three relays 1:-4, B-4 and E-4are effectively' in parallel with each other across the amplifieroutput. The function of the biasing resistors 213, 213b and 213e issimply to reduce the D.C. voltage applied across the respective relaycoils to an acceptably low level.

Normally, all three alarm tones (tire, burglary and plant equipment) arereceived and they keep the respective reed relays F-4, B-4 and E-4operating continuously. Each reed relay, when so energized, closes itsinternal contacts f-S and f-6, b5 and b-6, or e-5 and e-6 forapproximately 20% of each cycle of the respective incoming alarm tone.

Referring to the fire alarm reed relay F-4, its Contact f-S is connecteddirectly to the aforementioned line 196. Under normal conditions itscontact f-6 is connected through a series circuit composed of a resistor214, a condenser 215 and contacts 222, 223 to ground. The contacts f-Sand f-6 of reed relay F-4 charge condenser 215 through resistor 214 soas to maintain `a voltage at the junction point 217 between them ofsubstantially -12.8 volts. l

A rectifier diode 218 is connected between this junction point 217 andthe base of a transistor F-7. A rectifier diode 219 and an adjustableresistor are series-connected between juncture 217 and the base of asecond transistor F-S. The collector of transistor F-7 is connectedthrough a resistor 221 to line 196. The emitter of transistor F-7 isconnected directly to the collector of transistor F-S. The emitter oftransistor F-S is connected to one terminal `of the coil of an alarmrelay F-9, the other terminal of this coil being connected to the lowerterminal of condenser 215.

With this arrangement, the transistors F-7 and F-S are connected inseries, each as an emitter follower. Normally, both diodes 218 and 219conduct, passing the 12.8 volt D.C. signal from junction point 217 tothe respective transistors F7 and F-S. Because both transsistors F-7 andF-S are emitter followers, the voltage applied across the coil of relayF-9 is also approximately 12.8 volts, which is effective to operate thisrelay.

The use of two transistors (F-7 and P S), where one would have suiced,through simple redundancy greatly enhances the reliability of thiscircuit.

Relay F-9 has a first set of contacts composed of a grounded mobilecontact 222, a normally-open xed contact 223 connected through the greenlamp 216 to line 196 and also connected to the lower terminal of thecoil of this relay, and a normally-closed fixed contact 224 connectedthrough a red indicator lamp 225 to line 196. Contact 224 also isconnected directly to a line 226 leading to a visual re alarm device.

Relay F9 also has a second set of contacts comprising a mobile contact227 and a normally-open xed contact 228, which are respectivelyconnected directly to lines 229 and 230` leading to an audible firealarm device.

When the coil of relay F-9 is energized as described, the followinghappens;

(l) The green indicator lamp 216 is energized through relay contacts 222and 223, and the lower end of relay coil F-9 is grounded through thesesame contacts;

(2) The red indicator lamp 225 is out because relay contacts 222 and 224are open, and the visual lire alarm device on line 226 is keptde-energized for the same reason;

(3) The audible fire alarm device is kept de-energized due t-o relaycontacts 227 and 228 being closed.

A reset relay F-10 is associated with the alarm relay F-9. The lower endof the coil of relay F-l()` is connected directly to line 196. The upperend of this relay coil is connected through a normally-open reset switch231 to line 226. Relay F-10 has three sets of contacts. The first setcomprises a mobile contact 232 connected directly to line 226 and `anormally-open fixed contact 233 connected to the upper end of the coilof relay F-10. The second set comprises a mobile contact 234 connectedto Ztl line 230 and a normally-open fixed contact 235 ccnnected to line229. The third set comprises a grounded mobile contact 236 and anormally-open xed contact 237 connected to the lower end of the coil ofrelay F-9 and to the line 196 through the green lamp 216.

Normally (i.e., as long as the lire alarm tones are being received atthe alarm central station), the reset switch 231 is open, relay F-9 isenergized, and relay F-10 is de-energized.

When a lire alarm condition occurs at the customers premises, this willstop the lire alarm tone, as described. Consequently, relay F-9 willbecome cle-energized, turning off the green lamp 216 and turning on thered lamp 225 and also producing an audible alarm by way of lines 229 and230 and a visual alarm over line 226 which will be noticed by theoperator at the alarm central office. The operator now closes the resetswitch 231 momentarily, completing an energization circuit for the coilof the relay F-10 by way of line 196, the coil of relay F-lt), resetswitch 231, line 226, and the F-9 relay contacts 224 land 222 to ground.

When the reset relay F-lt) becomes energized, its contacts 236 and 237close, connecting the lower end of the coil of alarm relay F-9 to groundso that the latter will be energized when the tire alarm tone reappears.Also, the closing c-f the F10 relay contacts 236, 237 turns on the greenlamp 216 again. The red lamp 225 remains on as long as relay coil F-9remains deenergized. This is the stand-by condition, with both the redand green lamps 225 and 216 on.

Also, when the coil of reset relay F-10 is energized, its contacts 234and 235 close, shorting lines 229 and 230 and thereby de-energizing thebell or other audible alarm device operated by these lines.

Also, when the coil of reset relay F-10 is energized, its contacts 232and 233 close, completing a holding circuit for maintaining F-l()energized, independent of the reset switch 231, by Way of line 196,relay coil F-10, F-10 relay contacts 233 and 232, line 226, and F-9relay contacts 224 and 222 to ground. Therefore, relay F-10 will remainenergized, even after the reset switch 231 is released by the operatorand opens again, until relay F-9 becomes energized again.

When the lire alarm condition at the customers premises has beencorrected and the re alarm tone is restored, this re-energizes the coilof alarm relay F-9 with the following results:

(1) The F-9 relay-contacts 222 and 223 close again, breaking the holdingcircuit for the coil of reset relay F-10 and causing the latter tobecome de-energized (reset switch 231 being open);

(2) The red lamp 225 goes out and the green lamp 216 stays on,indicating that the lire alarm system has been restored to the no-alarmcondition;

(3) The lower end of the coil of alarm relay F-9 is connected to groundthrough its now-closed contacts 223 and 222 for normal energization ofF-9;

(4) The F-9 relay contacts 227 and 228 close to keep the audible firealarm device connected across lines 229 and 230 from sounding;

(5) The opening of the F-9 relay contacts 224 and 229 turns off thevisual re alarm device connected to line 226.

The reedrelay B-4 operated by the incoming burglar alarm tones has anamplier and alarm relay arrangement which is identical to that describedin detail for the fire alarm reed relay 1:*4. This amplifier and alarmrelay arrangement will not be described in detail. Correspondingelements in this arrangement are 4given the same reference numerals asin the tire alarm circuit, with a b subscript added. The transistors inthis burglar alarm amplifier are designated B-7 and B-S, respectively,and the relays B-9 and B-10.

The reed relay E-4 operated by the plant equipment alarm tones has anamplier and alarm relay arrangement which is identical to that for thefire alarm reed relay F-4, also. Corresponding elements in the plantequipment alarm circuit have the same reference numerals as those in thefire alarm circuit, with an e subscript added. The transistors in thisplant equipment alarm circuit are designated E-7 and E8, and the relaysE-9 and E-lf), respectively.

The lines 229, 230 and 229b, 23011 and 229e, 230e may all be connectedto a gong or other audible alarm device which will operate in responseto any of the three types of alarm conditions so as to alert theoperator at the alarm central station.

The occurrence of such an alarm condition and its detection at the alarmcentral station also operate a recording apparatus (not shown), whichautomatically prints a record identifying the customers premises wherethe alarm condition has occurred, the type of alarm, the time of thealarm, and other pertinent information.

From the foregoing detailed description it Will be apparent that thespecific system of FIGS. 1-8 is particularly Well adapted for theaccomplishment of all of the stated objects of this invention. However,it is to be understood that various modifications, omissions andrefinements which depart from this specific embodiment may be adoptedwithout sacrificing the essential operating characteristics desired. Forexample, if very high quality rejection filters are used at the oppositeends of the telephone line the hybrids may be omitted as not absolutelynecessary to provide the desired separation between the alarm tonesignals and the audio program signals.

SYSTEM OF FIGURES 9-13 A second system in accordance with the presentinvention is illustrated in FIGS. 9-13. This system accomplishes many,but not all, of the stated objects of this invention and therefore isconsidered less desirable than the system of FIGS. 1-8, althoughoffering numerous significant advantages over prior alarm signalingsystems.

Referring to FIGS. 9-13, the portion included within the dashed-lineenclosure 310 in FIG. 9 is identified as program and alarm central, theportion enclosed within the dashed-line enclosure 311 (FIG. 12) is atthe head oice of the store system, or alternatively, the school boardoffices if the arrangement is incorporated in such a system. The portionenclosed within the dashed-line enclosure 312 (FIG. 13) is the alarmsignaling circuitry and the audio program receiving unit at thecustomers premises, such as a store or school, and it is to beunderstood that there may be asvmany of these units as desired.

Dealing first with a description of the audio program source at thealarm central station (FIG. 9), a tape deck 313 is provided for tapedmusic. for distribution to the various program receiver units 312 at thevarious customers premises. This audio program material passes throughcompression amplifier 314, cathode followery 315, line transformer 316and distribution amplifier 317, all of which are conventional inconstruction.

From the distribution amplifier 317, these audio program signals are fedto an output transformer 318 and thence by a private telephone linehaving just two wires 319, to the program receiver units 312 (FIG. 13).

It is desirable to supply a further tape deck 320 (FIG. 9) upon whichtaped speech announcements rmay be recorded, these speech announcementspassing through a switching module 321 which will hereinafter bedescribed, through a similar compression amplifier 314a and cathodefollower 315a to line transformer 316a and distribution amplifier 317a.

The output from the distribution amplifier 317a is fed also to theoutput transformer 318, it being understood that, due to the switchingmodule 321, either the music tape deck 313 or the speech tape deck 320only is in use at one time.

It is, of course, desirable to be able to cut in voice from the headoffice location 311 (FIG. 12) and in this connection a microphone 322 isutilized together with line amplifier 323, the output being fed throughthe two wires 324 of a telephone line from the head ofiice (FIG. 12) tothe input transformer 325 of the switching module 321 at the alarm andprogram central station 310 (FIG. 9).

The switching module 321 is used basically to intersperse speechannouncements from the tape deck 320 with musical selections from thetape deck 313 and the switching module accomplishes this by sensing thesilence period between the musical selections and then, depending uponthe settings, cutting in the speech tape deck 320.

As an example, if the integrating control is set at four, then fourmusical selections will pass and then the music tape deck 313 will stopand the speech tape deck 320 will start.

Reference character 326 in FIG. 9 indicates a message interlock relaywhich is used to prevent the operation of the microphone 322 so long asthe speech tape deck 320 is operating. The voltage of the power supplyextends via the telephone line wires 324 back to the head ofce location311 (FIG. 12) and is interconnected with the operating control 327 ofthe microphone 322 there, which prevents it from cutting in as long as amessage is emanating from the speech tape deck 320. This is to preventspeech emanating from two sources simultaneously but, of course, themicrophone 322 at the head office can be used while the music tape deck313 is in operation.

Dealing next with the unit 312 (FIG. 13) at the customers premises, thetwo wires 319 of the telephone line extending between the program andalarm central station and the customers premises enter the unit by meansof an input transformer 328. The incoming audio program signals pass tothe local program amplifier 329 and thence to the various speakers (notindicated) of the sound system at the customers premises.

Dealing next with the alarm signaling system at the customers premises(FIG. 13), reference characters 330, 331 and 332 indicate oscillatorencoding modules, the details of which are shown in FIG. 10. These arein effect tone generators, each of which generates a tone at anextremely precise distinctive frequency. Preferably these alarm tonesmay have closely spaced, separate and distinct frequencies within thefrequency range specified in the description of the system of FIGS. 1-8.These alarm tones pass through a line amplifier 334 and thence tocorresponding decoder modules 330, 331 and 332 situated in the unit 312at the customers premises and corresponding decoder modules 330", 331"and 332" situated in the program and alarm central unit 310 (FIG. 9).

In the specific system shown, three encoders are provided Withcorresponding decoders but it will be appreciated that any number can beincorporated depending upon the number of different alarm servicesdesired.

The encoder 330 is represented as the police alarm module and may coverthe store safe, doors, windows, and other areas desired to be protectedagainst burglary.

The encoder 331 is designated as the fire alarm module and m'ay coverspringler operation, smoke sensing devices and other fire detectionapparatus.

The plant supervision oscillator 332 is designed to protect such itemsin supermarkets as cold box thermostats, furnace pilot-off detector',and primary power failure detector.

The above are representative only of the various elements which may beincorporated in series with the encoders and are identified as sensingelements 333 in all cases and it will be noticed that these sensingelements shown are in series with the output to the line amplifier 334and are illustrated as contacts shown in the closed position, whichmeans that the alarm tones generated by the encoders pass through thesensing elements to the line

9. A LINE FAULT SUPERVISION ARRANGEMENT IN A SIGNALING SYSTEMCOMPRISING: A TWO-WIRE TELEPHONE LINE; A FIRST DIRECT CURRENT SOURCE ATONE END OF THE LINE FOR APPLYING A FIRST D.C SUPERVISORY CURRENT TO ONEWIRE OF THE LINE; FIRST RESISTANCE MEANS AT THE OPPOSITE END OF SAIDLINE TERMINATING SAID ONE WIRE TO GROUND FOR D.C.; A SECOND DIRECTCURRENT SOURCE AT SAID ONE END OF THE LINE FOR APPLYING A SECOND D.C.SUPERVISORY CURRENT TO THE OTHER WIRE OF SAID LINE; SECOND RESISTANCEMEANS AT THE OPPOSITE END OF SAID LINE TERMINATING SAID OTHER WIRE TOGROUND FOR D.C.; AND MEANS AT SAID ONE END OF THE LINE OPERABLE INRESPONSE TO AN ABNORMAL SUPERVISORY CURRENT IN EITHER WIRE TO INDICATE AFAULT ON THE LINE.
 16. AN ALARM SIGNALING SYSTEM FOR SIGNALING AN ALARMFROM A REMOTE STATION TO A CENTRAL STATION, SAID SYSTEM COMPRISING: